Fuel aggregates for motor vehicles comprise a fuel cell in which electric energy is produced, commonly by the use of hydrogen and oxygen. If necessary, a reformer precedes the fuel cell. By means of the reformer, hydrogen can be obtained from conventional fuels such as gasoline, diesel oil or methanol, which is then supplied to the fuel cell. Because of the reformer preceding, fuel aggregates can be used in motor vehicles without the requirement of a supply of hydrogen being guaranteed all over. Generally, controllable valves are required between the reformer and the fuel cell to be able to supply the fuel cell with the appropriate amount of oxygen and hydrogen. Such valves, which may have the form of flap valves, for example, are throttle valves, for example, which serve as control or turnoff valves or also as bypass valves. Further, flap valves are also required if the fuel aggregate does not have a reformer and the fuel cell is rather supplied with hydrogen from a hydrogen tank. Then, the valves are arranged between the hydrogen tank and the fuel cell.
Fuel aggregates require that the utilized valves are able to close a flow channel extremely tightly. This is required for the use of hydrogen, for example, because mixtures of hydrogen and air may explode even with low shares of hydrogen. Furthermore, very high tightnesses of the valves are required since hydrogen is a fluid gas, i.e., a gas with very small molecules.